How do you share a blender.file?
Before uploading make sure to pack all external data.
Images used as textures, backgrounds or environments do not get saved into the .blend file by default. To include those as part of the file you have to Pack them. In the File menu press File&gt;External Data&gt;&quot;Pack all into .blend&quot;

PLEASE NOTE:
Image sequences, video files and Simulations Cache Folders will not be packed. For those it would be better to place them in a common folder along with the blend file and zip them (or bundle them with any other packaging software). And share the whole folder. For convenience you might also want to make the blend file work with relative paths, so that you don't have to re-create the folder structure used on the original computer.
For more info, read this page form the manual: https://docs.blender.org/manual/en/dev/editors/info/file.html?highlight=find%20missing%20files#file
To save the baking cache for physics simulations see: Can I save the baking cache? or Is there a way to save a baked cloth simulation (in .blend file or to disc)?

If the question is where to host a file for a question asked on this site please use:
https://blend-exchange.giantcowfilms.com/

Note
https://blend-exchange.giantcowfilms.com/ can olny host .blend files (not zipped folders) used as part of questions and answers on this site, and they have to be smaller than 30MB. To share larger files or bundled content on zipped files there are numerous free or paid websites and services. But that part of the question is beyond the scope of this site, so do your own research.